The Fine Old Lafferty Name  

According to Bell "The Surnames of Ulster", Lafferty is exclusively an Ulster name. In 1900 it was found only in Donegal, Derry, and Tyrone. It comes from O'Laithbheartaigh, or "Bright Ruler". O'Lafferty or O'Laverty are Ulster forms of the Connacht name O'Flaverty or O'Flaherty. The F is aspirated or silent in Ulster Gaelic. Bell explains that O'Flynn in Ulster is O'Lynn for the same reason.

The O'Laffertys were a Donegal sept. The chief was the Lord of Aileach, famous for building the Grianan of Aileach at the head of Lough Swilly. The first of the name was Murchadh Ua Flaithbheartaigh, king of Tyrone, d 972. One of the chiefs was Macraith O'Laverty, d 1197, described by the Four Masters as the Tanist of Tyrone. This was shortly before the chieftancy of Tyrone passed to the O'Neills. They were driven from Donegal in the 13th century and settled near Ardstraw in Co. Tyrone.

He says Laverty is found in Antrim, and comes from MacLavertys, a sept of Clan Donald, hereditary speakers or heralds for the Lords of the Isles. Clan Donald claims the name was Fear Labhairt an Righ, The King's Speaker, but Black (the Scots expert) says it is Mac Fhlaithbheartaich, which is like the Irish name. The McLaffertys claim to be from the Kintyre branch of the MacDonalds and were later based in Islay. You find them in the mid 19th century in Antrim in the barony of Upper Dunluce.

Rev. James O'Laverty in his little booklet written in the late l800s states the following:
"The locality to which this surname originally belonged was Tir-Eoghain (now anglicized Tyrone (meaning Eoghain's country). Eoghain was a brother of Conall (who gave name to Tyrconnell). The original principality of Tyrone was much larger is size than the present day county Tyrone. Eoghain and Conall were sons of Niall of the Nine Hostages, monarch of Ireland from A.D. 379 to A.D. 406. Their descendants were, in after ages, known as the Northern Ha-Niall, while the descendants of the other sons who had parcelled among themselves Mealth were known as the southern Hy-Miall.

Paraphrasing Rev. O'Laverty's work, he continues by saying that the family name O'Flaherty or O'Laverty is descended from Aedh Allan, King of Ireland from A.D. 729 to A.D. 738. A Flaithbheartach who died A.D. 891 was a great grandson of Aedh Allan. However, the first to bear the surname was Flaithbeartach's grandson Murchadh Ua Flaithbheartaigh ("Ua" designating grandson of). Murchadh was King of Tyrone and died A.D. 972. This name is still common in the counties of Donegal, Derry and Tyrone but by an asperation of the initial F, is now anglicised Laverty or Lafferty. Ua Flaithbheartaigh is a Tyronian family, but assumed its anglicized form (Lafferty/Laverty) in more recent times.
 
And that is more than you may ever want to know about the surname Lafferty.